package com.hit.basmath.learn.others;

/**
 * 65. Valid Number
 * <p>
 * Validate if a given string can be interpreted as a decimal number.
 * <p>
 * Some examples:
 * <p>
 * "0" => true
 * " 0.1 " => true
 * "abc" => false
 * "1 a" => false
 * "2e10" => true
 * " -90e3   " => true
 * " 1e" => false
 * "e3" => false
 * " 6e-1" => true
 * " 99e2.5 " => false
 * "53.5e93" => true
 * " --6 " => false
 * "-+3" => false
 * "95a54e53" => false
 * <p>
 * Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:
 * <p>
 * 1. Numbers 0-9
 * 2. Exponent - "e"
 * 3. Positive/negative sign - "+"/"-"
 * 4. Decimal point - "."
 * <p>
 * Of course, the context of these characters also matters in the input.
 */
public class _65 {
    public boolean isNumber(String s) {
        s = s.trim();

        boolean pointSeen = false;
        boolean eSeen = false;
        boolean numberSeen = false;
        boolean numberAfterE = true;
        for (int i = 0; i < s.length(); i++) {
            if ('0' <= s.charAt(i) && s.charAt(i) <= '9') {
                numberSeen = true;
                numberAfterE = true;
            } else if (s.charAt(i) == '.') {
                if (eSeen || pointSeen) {
                    return false;
                }
                pointSeen = true;
            } else if (s.charAt(i) == 'e') {
                if (eSeen || !numberSeen) {
                    return false;
                }
                numberAfterE = false;
                eSeen = true;
            } else if (s.charAt(i) == '-' || s.charAt(i) == '+') {
                if (i != 0 && s.charAt(i - 1) != 'e') {
                    return false;
                }
            } else {
                return false;
            }
        }

        return numberSeen && numberAfterE;
    }
}
